1. Field of the Invention
The present invention relates to an inverter control system that controls an inverter circuit in order to drive a load such as a motor, in particular, relates to a resonant inverter control system that controls an inverter circuit provided with snubber capacitors for carrying out soft switching, and also relates to a resonant inverter apparatus that carries out soft switching in order to drive a motor used in an electric vehicle (EV), a hybrid vehicle (HEV), or the like.
2. Description of the Related Art
Technology for conventional inverter circuits for driving a load such as a motor is disclosed in U.S. Pat. Nos. 5,710,698, 5,642,273, and 5,047,913. According to these patents, as shown in FIG. 15, for example, a conventional example of a soft switching inverter comprises an inverter part using as switching elements IGBTs (insulated gate bipolar transistors) Q101 to Q106 connected to the motor 1, which comprises a three phase induced motor or a direct current brushless motor that serves as a load.
In the inverter, the IGBT Q101 to Q106 are connected at both terminals of the direct current power source 3 to form a three-phase bridge structure comprising a U phase, a V phase, and a W phase, and free wheeling diodes (FWD) D101 to D106 are connected between the collector terminals and emitter terminals of each of the IGBTs, with the object of circulating the regeneration energy that the load of the inductance of the motor 101 generates and the current energy accumulated in the load of the inductance. In addition, snubber capacitors C101 to C106, which are for absorbing a surge voltage applied across the collector terminal and the emitter terminal of the IGBTs during the turn-ON and turn-OFF of the IGBTs, are also connected between the collector terminals and emitter terminals of each of the IGBTs.
Furthermore, in the inverter, a smoothing capacitor C109 is connected to the direct current power source 103, and at the connection points of the center-taped voltage maintaining capacitors C107 and C108 that are connected serially to both terminals of the smoothing capacitor C109, from the respective connecting points of the U phase snubber capacitors C101 and C102, the V phase snubber capacitors C103 and C104, and the W phase snubber capacitors C105 and C106, bi-directional switch units SU101 to SU103 for running resonant current via the inductor are respectively connected to the inductor L101 that resonates with the snubber capacitors C101 and C102, the inductor L102 that resonates with the snubber capacitors C103 and C104, and inductor L103 that resonates with the snubber capacitors C105 and C106.
The structure described is also called an auxiliary free-wheeling arm linked snubber inverter, and in the soft switching inverter having the structure described above, when, for example, the IGBT Q102 is to be turned ON slightly after the IGBT Q101 is to be turned OFF, the charging current of the snubber capacitor C101 and the discharge current of the snubber capacitor C102 flow to the center-taped voltage maintaining capacitors C108 and C108 via the inductor L101, and at the same time, when the IGBTs Q103 and Q105 are to be turned ON slightly after the IGBTs Q104 and Q106 are to be turned OFF, the charging current of the snubber capacitors C104 and C106 and the discharge current of the snubber capacitors C103 and C105 is supplied from the center-taped voltage maintaining capacitors C107 and C108 via the inductors L102 and L103.
Therefore, the snubber capacitor will charge and discharge due to the resonant current of the snubber capacitor and the inductor, and thus in the case that the IGBT turns OFF and the snubber capacitor is charged, because of the delay in the rise of the voltage applied to the IGBT provided by the snubber capacitor due to the time constant, ZVS (Zero Voltage Switching) of the IGBTs is realized. In contrast, in the case that before the IGBT is turned ON the snubber capacitor discharges, the voltage and current applied to the IGBTs due to the free wheeling diode conduction falls to zero. Thereby, the loss that occurs during the turn-ON and the turn-OFF of the switching elements can be reduced because ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) of the IGBTs are realized.
FIG. 16 is also a conventional example of a soft switching inverter, also called an auxiliary resonant AC linked snubber inverter, and like the auxiliary resonant commutation arm linked snubber inverter in FIG. 16, comprises an inverter part in which the IGBTs Q101 to Q106 connected to free wheeling diodes D101 to D106 and snubber capacitors C101 to C106 are connected at both terminals of the direct current source 103 to form a three-phase bridge structure comprising a U phase, a V phase, and a W phase and a structure wherein the inductor L104 that resonates with the snubber capacitors C101 and C102, the inductor L105 that resonates with the snubber capacitors C103 and C104, and the inductor L106 that resonates with the snubber capacitors C105 and C106 are respectively connected between the connecting point between the U phase snubber capacitors C101 and C102, the connection point between the snubber capacitors C103 and C104 of the V phase, the connecting point between the snubber capacitors C105 and C106 of the W phase of the inverter and the bi-direction switching units SU104 to SU106 for providing a resonant current to flow via the inductors.
The difference in operation between the auxiliary resonant AC linked snubber inverter in FIG. 16 and the auxiliary resonant snubber inverter in FIG. 15 is only the paths of the current that charges and discharges the snubber capacitor, and the principle that the IGBTs, which comprise each of the switching elements, attain ZVS and ZCS is identical.
In the conventional example of a soft switching inverter such as that described above, forming the resonant circuit by snubber capacitors and each of the inductors is effective for making the loss during the turn ON and the turn OFF that occurs in the switching elements small because the current flowing to the IGBTs (switching elements) and the voltage applied to the IGBTs can be controlled.
However, because the core capacity required by the inductors is determined by the conducting peak current, the weight of the inductors and the volume of the inductors increases along with an increase in the controlled load current, and in particular, in the conventional example of the soft switching inverter that required three inductors through which a current equal to or greater than the load current can flow, there are the problems that decreasing the weight and down-sizing are not possible due to the increase in the weight and volume of the inductors.
In addition, clearly decreasing the weight and down-sizing is most effectively attained by reducing the number of inductors, but in carrying out soft switching after the number of inductors have been reduced, inverter control that is different from conventional technology is required, and thus there is the problem that the control device must be clarified.
In consideration of the problems described above, an object of the first embodiment of the present invention is to provide a resonant inverter control apparatus that can concretely control the resonant inverter having a reduced number of resonant inductors according to this operating principle to realize soft switching.
Furthermore, in a soft switching inverter apparatus of the first embodiment, during the turn-ON operation and turn-OFF operation of the main switching elements, by establishing resonance across the resonant inductor in the auxiliary circuit and the resonant capacitors connected in parallel to the main switching elements, the slope of the change of the voltage across terminals of the main switching elements becomes gentle and soft switching is realized.
However, in the case that the main switching elements are turned OFF from the state in which the main switching electrodes conduct a current, because immediately before the turn-OFF a load current was conducted to the main switching elements, even if more resonant current does not flow due to the auxiliary circuit, the charging and discharging of the capacitors between the terminals of the main switching elements are possible.
At the time that the current is conducted to the main switching element, when the auxiliary circuit is forced to conduct, the auxiliary circuit is connected in parallel to the load. Thereby, the equivalent increase in the current due to the auxiliary circuit being forced to conduct is superimposed on the load current flowing to the main switching element, and due to this increase in the current, the conducting loss of the main switching element increases.
Therefore, an object of the second embodiment of the present invention is to provide an inverter apparatus having a smaller loss than conventional technology and has a high efficiency.
According to the first aspect of the present invention, a resonant inverter control apparatus that controls an inverter circuit comprises six main switching elements (for example, IGTQ1 to IGTQ6 in the embodiments) connected to form a three-phase bridge; six free wheeling diodes (for example, free wheeling diodes D1 to D6 in the embodiments) and six snubber capacitors (for example, snubber capacitors C1 to C6 in the embodiments) respectively connected in parallel between two terminals of the main switching elements that are made conductive or non-conductive by the switching control; main switching circuits in which each of the connection points between three groups of main switching circuits that form each phase of a three phase bridge structure (for example, a bridge circuit 2B1 in the embodiments) connected serially by pairs to each end of a power source serve as three phase output terminals for connecting the load (for example, the motor in the embodiments); and an auxiliary switching circuit in which six auxiliary switching elements that force current to flow in one direction are connected to form a three phase bridge connection and resonant inductances (for example, resonant inductance Lr in the embodiments) is connected to the bridge circuit (for example, the bridge circuit 2B1 in the embodiments) that respectively connects each connection point between said auxiliary elements to said three phase output terminals, comprising, a three phase control device (for example, the control CPU 5 in the embodiments) that outputs a three phase control signal that serves as a reference for controlling said main switching elements of said inverter circuit, six voltage measuring devices (for example, voltage sensors Vs1 to Vs6 in the embodiments) that measure the voltage across two terminals of said main switching element, zero voltage detecting device (for example, zero voltage detecting device 7 in the embodiments) that detects that the voltage across any two terminal of said six main switching elements is zero by the output of said voltage measuring device, four current measuring devices (for example, current sensors Is1 to Ts4 in the embodiments) that respectively measures the three phase current flowing to said load and the induced current flowing to said inductors, a resonant current arrival determining device (for example, a resonant current arrival determining device 8 in the embodiments) that calculates the absolute value of the maximum value of said three phase current and whether or not the induced current is larger than this maximum value based on the output of said current measuring device, and a drive signal generating device (for example, a drive signal generating device 6 in the embodiments) in which a switching control signal that forces conduction across said two terminals of said main switching element is output when the zero voltage detecting device detects that a voltage across said two terminals of the switching elements to be controlled is zero based on the control by said three phase control signal, and a switching control signal that interrupts the conduction across said two terminals of said main switching element that is the phase of the main switching element corresponding to this maximum value and has two terminals in a conducting state is output when said resonant current arrival determining device has determined that said induced current is larger than the absolute value of the maximum value of said three phase current.
By constructing the resonant inverter control apparatus as described above, by using the resonant current arrival determining device, whether the induced current is larger than the load current is detected, a turn OFF operation is carried out on the main switching element that is currently in a conducting state, the zero voltage detecting means then detects that the voltage across the terminals of a main switching element that resonates with the snubber capacitor and inductors has fallen to zero, and next a turn ON operation of the main switching elements which are currently in a non-conducting state connected serially to the main switching elements that are turned OFF is carried out. Therefore, in the turned OFF main switching elements, ZVS and ZCS can be realized, and thus control becomes possible that reduces the loss in the inverter circuit to a minimum.
According to the second aspect of the present invention, in the resonant inverter control apparatus, when, in the inverter control apparatus in the first aspect, the main switching elements are separated into first, second, and third upper level switching elements (for example IGBT Q1, Q3, and Q5 in the embodiment) corresponding to each phase of the three phase bridge and fourth, fifth, and sixth lower level switching elements (for example, IGBT Q2, Q4, and Q6) corresponding to each phase of the three phase bridge, and the auxiliary switching elements are separated into the seventh, eighth, and ninth switching elements (for example, IGBT Q7, Q9, and Q11 in the embodiment) that are respectively connected to the three phase output terminals that conduct only in the direction in which the current flows to each of the connecting points between the auxiliary switching elements, and the tenth, eleventh, and twelfth switching elements (for example, IGBT Q8, Q10, and Q12) that are respectively connected to the three phase output terminals that conduct only in the direction in which the current flows out from each of the connection points between the auxiliary switching elements, the drive signal generating device outputs switching control signals that force the seventh, eighth, and ninth switching elements to conduct in synchronism with a three phase control signal that directs the output of a switching control signals that force the first, second, and third switching elements to conduct, and outputs switching control signals that force the tenth, eleventh, and twelfth switching elements to conduct in synchronism with the three phase signals that direct the output of switching signals that force the fourth, fifth, and sixth switching elements to conduct.
By constructing the resonant inverter control apparatus as described above, by using the control signals for controlling the main switching elements, it is possible to simply control an auxiliary switching element by controlling only one resonant inductor using the control signals for controlling the main switching elements.
According to the third aspect of the invention, in the above resonant inverter control apparatus, for the signals of each phase of the three phase control signal, when the case in which the switching control signal forces conduction across the two terminals of the first, second, and third switching elements and the interrupts the conduction across the two terminal of the fourth, fifth, and sixth switching elements is represented by the logical value xe2x80x9c1xe2x80x9d and the case in which the switching control signals force conduction across the two terminals of the fourth, fifth, and sixth switching elements and interrupts the conduction across the two terminals of the first, second, and third switching elements is represented by the logical value xe2x80x9c0xe2x80x9d, the exclusive logical OR of the logical values representing the three phase signals of the three phase control signal output by the three phase control device is always the logical value xe2x80x9c1xe2x80x9d.
By constructing the resonant inverter control apparatus as described above, the resonance operation by the snubber capacitors and inductors can be reliably activated, and in the control of a three phase inverter circuit, the combination state of the signals for each phase of the three phase control signals becomes (Us, Vs, Ws)=(0, 0, 0) or (1, 1, 1), and thereby the occurrence of hard switching can be suppressed.
According to the fourth aspect of the present invention, in the above inverter control apparatus according to the third aspect, the state transitions of the three phase control signals output from the three phase control device satisfy either the case that the logical OR of the logical values that represent the signals for each of the phases of the three phase control signals after the state transition are identical to the logical OR of the logical values that represent the signals for each of the phases of the three phase signal after the state transition, or the case in which the logical values that represents the signals of each of the phases of the three phase control signals after state transition are inversions of the logical values representing the signals of each of the phases of the three phase signals after the state transition.
By constructing the resonant inverter control apparatus as described above, the resonance operation by the snubber capacitors and inductors can be reliably activated, and in the control of a three phase inverter circuit, before and after the state transitions of the three phase control signals, for example, transiting from (Us, V, Ws)=(1, 0, 0) to (Us, Vs, Ws)=(1, 1, 0), and thereby, it is possible to suppress the occurrence of hard switching due to only the signal for one phase among the three phases not changing.
According to the fifth aspect of the present invention, in the above inverter control apparatus, when the output time during which the three phase control device continues to output identical three phase signals is greater than the time during which the induced current flows through the inductors, and the maximum time of the conduction continuation time of the auxiliary switching element is equal to or less than the time during which the induced current flows through the inductors when any of the three phase currents is flowing at a maximum, the drive signal generating device outputs to the auxiliary switching element in a non-conducting state a switching control signal that forces the auxiliary switching element to conduct in synchronism with the three phase control signal that directs the output of a switching control signal to the main switching element, or outputs a switching control signal to the auxiliary switching elements in a conducting state a switching control signal that forces the interruption of conduction of the auxiliary switching elements when the maximum time of the conducting continuation time of the auxiliary switching element has been attained in the case that the output time of the three phase control signal is longer than the maximum time for the conduction continuation time of the auxiliary switching elements, or outputs a switching control signal that forces the interruption of the conduction of the auxiliary switching elements in synchronism with the three phase control signal that directs the output of the switching control signals to the main switching elements in the case that the output time of the three phase control signal is shorter than a maximum time for the conduction continuation time of the auxiliary switching elements.
By constructing the inverter control apparatus as described above, the switching operation in the auxiliary switching elements is carried out when current is not flowing in the auxiliary switching elements, that is, ZCS can be realized with auxiliary switching elements.
According to the sixth aspect of the present invention, is a resonant inverter control apparatus comprising an inverter circuit (the main circuit 2A in the embodiment) in which a direct current output by a power source (power source VB in the embodiment) is converted to a three phase alternating current and supplied to a three phase motor (the motor 1 in the embodiment), a resonant circuit (auxiliary circuit 2B in the embodiment) that is connected to the output terminal of the inverter circuit, and a control circuit (control circuit 3 in the embodiment) that control the resonant circuit and the inverter circuit. The inverter circuit comprises three phase main circuits connected in parallel to three circuits, one for each phase, wherein a main switching element (for example, the main switching element Q1 in the embodiment) that is connected to the plus terminal of the power source and the main switching elements (for example, the switching element Q2 in the embodiment) that are connected to the minus terminal of the power source are connected in series, and connected in parallel to diodes (for example, diodes D1 and D2 in the embodiment) respectively connected to these two main switching elements; capacitors (capacitors C1 to C6 in the embodiment) that are connected in parallel to the main switching elements in each of the circuits for each phase; load current sensors (load current sensors Is1, Is2, and Is3 in the embodiment) that detect a load current (I1, I2, and I3 in the embodiment) flowing across main connection points (main connection points PSU, PSV, and PSW in the embodiment), at which two main switching elements in each of the circuits for each phase are connected together, and the motor; and cross-terminal voltage sensors (the cross-terminal voltage sensors Vs1 to Vs6 in the embodiment) that detect the cross-terminal voltage (the cross-terminal voltages V1 to V6 in the embodiment) of the main switching elements in the each of the circuits for each phase. The resonant circuit comprises auxiliary connection points (the auxiliary connection points PHU, PHV, and PHW in the embodiment) in which three auxiliary circuits, one for each phase (for example, the auxiliary circuit for the phase 3U), connected serially to two auxiliary switching elements (for example, auxiliary switching element blocks B7 and B8 in the embodiment) that allow a current to pass only in one direction are connected in parallel, and two auxiliary switching elements in each of the auxiliary circuits for each phase are connected together; three phase auxiliary circuits connected to the main connection points of the inverter circuit; resonant inductors (the inductor Lr in the embodiment) connected between the auxiliary connection points in the auxiliary circuits for each phase and the terminals on the opposite side; and a resonant current sensor (resonant current sensor Is4 in the embodiment) that detects a resonant current (the resonant current I4 in the embodiment) flowing to the inductor. The control circuit comprises a zero voltage detecting device (the zero voltage detecting device 8 in the embodiment) that detects whether or not the cross-terminal voltage detected by each of the cross-terminal voltage sensors is zero and outputs a zero voltage detection signals (the zero voltage detection signals z1 to z6 n the embodiment) that corresponds to each of the cross-terminal voltages in the case that they are zero; a resonant current arrival determining device (the resonant current arrival determination device 7 in the embodiment) that determines whether or not the resonant current detected by the resonant current sensors is larger than the load current detected by the load current sensors and in the case that they are larger outputs an arrival determination signal (the arrival determination signal I in the embodiment); a drive signal generating device (the drive signal generating device 6) that generates a main drive signal (the main drive signals S1 to S6 in the embodiment) that turns OFF the main switching elements to a non-conducting state when the resonant current arrival determination device has output an arrival determination signal, generates a main drive signal that turns ON the main switching elements to a conducting state when the zero voltage detecting device has output a zero voltage detection signal corresponding to each cross-terminal voltage, generates an auxiliary drive signal (auxiliary drive signals S7 to S12) that turn ON the auxiliary switching elements at a predefined switching timing, and turns OFF an auxiliary switching element that is in a conducting state after a predetermined on continuation time has passed from the predefined switching timing; and current conducting device determining devices (the current conducting device discrimination devices 16U, 16V, and 16W) that determine whether or not a current is flowing in any of the main switching elements or diodes in each of the circuits for each phase in the inverter circuit. The drive signal generating device comprises a resonant action prohibiting device (the resonant operation prohibiting device 17 in the embodiment) that prohibits the generation of an auxiliary drive signal that turns ON a corresponding auxiliary switching element in the resonant circuit during the turn-OFF of the main switching element in the case that the current conducting device determination device has determined that a current is flowing in a main switching element.
According to the structure described above, the current conducting device determination device determines whether there is a current flowing in any of the main switching elements or diodes in each of the main circuits for each phase in the inverter circuit, and the resonant action prohibiting device prohibits the generation of an auxiliary drive signal that turns ON a corresponding auxiliary switching element in the resonant circuit while the main switching element is turning OFF in the case that the current conducting device determination device has determined that a current is flowing in a main switching element.
Therefore, soft switching control becomes possible without an unnecessary resonant current flowing. Thereby, the loss in the main switching elements, the auxiliary switching elements, and the resonant inductors can be greatly reduced and the efficiency increased.
In addition, in a collective resonant snubber inverter, because two phase switching in the resonant operation is necessary in the resonance operation and one phase switching is impossible, in space vector control, the 6 output voltage vectors V1 (1, 0, 0), V2 (0, 1, 0), V3 (1, 1, 0), V4 (0, 0, 1), V5 (1, 0, 1) and V6 (0, 1, 1), whose angles differ from each other by xcfx80/3 [rad] and which are represented by the three phase control signals depending on the pattern of the switching control, are switched and output depending on the pattern of the switching control of the inverter circuit. During the switching of the output voltage vector, a reverse voltage vector in which the output voltage vectors before switching and after switching differ by a xcfx80[rd] angle is output at a predetermined time, and subsequently the output voltage vector must be output after switching. In this switching of the output voltage vector, there is the restriction that it cannot be switched to the neighboring output voltage vector. However, according to the structure described above, because the operation of the resonant circuit is prohibited, the reverse voltage vector is not output, switching with only one phase becomes possible, switching the neighboring output voltage vector becomes possible, and thus the degree of freedom of the control improves.
According to the seventh aspect of the present invention, the current conducting device determining device of the first aspect comprises a current conduction direction determining device (the current conduction direction determining device 18 in the embodiment) that determines the direction that a load current detected by a load current sensor is flowing; and a logic processing device (the logic processing device 19 in the embodiment) that determines whether or not a current is flowing in any of the main switching elements or diodes in each of the main circuits for each phase in the inverter circuit based on the direction in which the load current determined by this current conduction direction determining means is flowing and the main drive signal generated by the drive signal generating device.
According to the above structure, the current conduction direction determination determines the direction that a load current detected by a load current sensor is flowing and the logic processing device determines whether or not a current is flowing in any of the main switching elements or diodes in each of the main circuits for each phase in the inverter circuit based on the direction in which the load current determined by this current conduction direction determining means is flowing and the main drive signal generated by the drive signal generating device.